Large, two dimension, screen for converting an optical image projected on one side to an identical infrared image display on the other side

ABSTRACT

A screen panel having conductive lattices, such as a copper plate, juxtaposed on each side of a dielectric substrate. The back side of the substrate and the conductive lattice thereon is covered with some photoconductive material, such as cadmium sulphide. The front side of the substrate and the conductive lattice thereon is covered with an infrared emitting substance of electrically resistive material having a high thermal emissivity, such as resistive black or a carbon slurry paint. A power supply is connected across the lattices on each side of the substrate and a conductor is inserted through the substrate for conductively connecting the photoconductive material and the electrically resistive material. An electrical circuit is formed that includes the voltage source, the back lattice, the photoconductive material, the conductor through the substrate, the electrically resistive material, and the front lattice, all connected in series. Light intensity, according to an image pattern projected on the back of the panel, lowers the electrical resistance of the photoconductor material. Lowering of the resistance in the photoconductive material causes increased current flow in the electrical circuit, and thus through the electrically resistive material on the front of the panel. Increased current flow in the electrically resistive material causes a temperature increase therein, and thus a pattern of infrared energy is emitted from the resistive material on the front of the panel in proportion to the visible light displayed on the back of the panel.

United States Paten 1191 Bly [75] Inventor: Vincent T. Bly, Alexandria,Va.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

[22] Filed: May 2, 1972 [21] Appl. No.: 249,572

[52] US. Cl ..250/83.3 HP, 250/83.3 l-I, 250/84,

, 250/211 R 51 Int. Cl ..G0lj 1/02 [58 Field of Search ..250/84, 83.3P1, 83.3 HP,

[56] References Cited UNITED STATES PATENTS 2,747,104 5/1956 Jacobs..250/211 R X 2,883,556 4/1959 Jenny et al 2,985,757 5/1961 Jacobs et al..250/211 R X Primary ExaminerArchie R. Borchelt A tt0rney-Harry M.Saragovitz, Edward J Kelly, Herbert Berl et al.

1451 May 22, 1973 [5 7 ABSTRACT A screen panel having conductivelattices, such as a copper plate, juxtaposed on each side of adielectric substrate. The back side of the substrate and the conductivelattice thereon is covered with some photoconductive material, such ascadmium sulphide. The front side of the substrate and the conductivelattice thereon is covered with an infrared emitting substance ofelectrically resistive material having a high thermal emissivity, suchas resistive black or a carbon slurry paint. A power supply is connectedacross the lattices on each side of the substrate and a conductor isinserted through the substrate for conductively connecting thephotoconductive material and the electri cally resistive material. Anelectrical circuit is formed that includes the voltage source, the backlattice, the photoconductive material, the conductor through thesubstrate, the electrically resistive material, and the front lattice,all connected in series. Light intensity, according to an image patternprojected on the back of the panel, lowers the electrical resistance ofthe photoconductor material. Lowering of the resistance in thephotoconductive material causes increased current flow in the electricalcircuit, and thus through the electrically resistive material on thefront of the panel. Increased current flow in the electrically resistivematerial causes a temperature increase therein, and thus a pattern ofinfrared energy is emitted from the resistive material on the front ofthe panel in proportion to the visible light displayed on the back ofthe panel.

12 Claims, 3 Drawing Figures INFRARED ENERGY PAIENIED m2 2 I975 FIG. 1

FIG. 2

LARGE, TWO DIMENSION, SCREEN FOR CONVERTING AN OPTICAL MAGE PROJECTED ONONE SIDE TO AN IDENTICAL INFRARED IMAGE DISPLAY ON THE OTHER SIDEBACKGROUND OF THE INVENTION This invention is in the field of convertinga visible image into an infrared image over a large area.

There is a need for life size, or near life size, panels for displayinginfrared images, also known as thermal images, for evaluating infraredsystems at normal focusing distances. Panels as large as feet X 25 feetand larger are meeded.

To provide large area panels for converting visible light to infraredradiation, amplification of the light signal is required since therequired concentration of visible light would be 1,000 foot-candles ormore; if no amplification was available. Furthermore, it is extremelydifficult to provide aninput illumination level above 10 foot-candles,over surfaces of these dimensions. In this invention, the relativelysmall. light signal modulates power, which is externally supplied: tothe panel to provide the necessary amplification.

SUMMARY OF THE INVENTION tion to its temperature, iscoatedover thelattice and;

substrate on the front of the panel. Conductive connections are formedthrough the. substrate at equal, distances from the conductive lattices.Theseconductive connections electrically connect the, photoconductivematerial and the resistive black. A power supply is con-' nected acrossthe lattices onthe front: of the panelto the lattice on the back of thepanel. Lightimpinging on the back of the panel lowers the, resistance ofthephotoconductive material, thus causingincreased current through thecircuit formed by the photoconductive material, the conductiveconnection through the substrate, and the resistive black. Increasedcurrent flow through the resistive black raises-its temperature, causingmore infrared-energy to be emitted therefrom. Therefore, infrared energyis emittedfrom the front surface in proportion to the intensity of thevisible image impinging on the back of the panel.

It is an object of this invention to provide a mosaic array of elementsincorporatinga photoconductor. and an emitting surface, such that whenthe photoconductor is modulated by a light image, the image is emittedfrom the emitting surface in the infrared spectrum.

BRIEF ILLUSTRATION OF THE DRAWINGS FIG. 1 illustrates a plan view of thefront side of the panel of this invention;

FIG. 2 shows a sectional view of the panel taken through 2-2 of FIG. 1;and

FIG. 3 shows a schematic diagramof the electrical circuit formed bymaterials and electrodes on the panel DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENT Referring now to FIGS. 1 and, 2, a portion of valarge screen panel 10 of the present invention is shown. The panel 10may, for instance, be as large as 10 feet X 25 feet or perhaps larger.Panels of this size require active amplification of the very weakvisible light that is imaged on the back side of panel 10. Theamplification is possible by the specific arrangement of materials andvoltage connections as discussed hereinbelow. Panel 10 is formed byconductive lattices l2 and 20 laid on opposite sides of a dielectricsubstrate 22. Lattice 12 is on the front side of panel 10 and isdesignated as the front conductive lattice. Lattice 20 is on the backside of panel 10 and is designated as the back conductive lattice.Lattices 12 and 20, are juxtaposed directly opposite each other onsubstrate 22, forming a matrix of individual cells of square conductinggrids on each side of panel 10. These grids may be made of copper. Inthe center of each square, a hole 14 is drilled and some conductor isplaced therein. The conductor may be a conducting pin inserted in thehole, or the hold could be made conductive by electroless plating. Hole14 could also be formed by mechanically drilled or chemically etched anda rivet or eyelet passed therethrough with a conductive paste, such asliquid aluminum, placed inside the rivet or eyelet and then squigged offthe front and back of the panel. A layer of photoconductive material 18is deposited on the backside of the panel, covering both lattice 20 andsubstrate 22. The photoconductive material may be cadmium sulphide, butis not limited tocadmium sulphide. The photoconductive material couldalternately be cadmium sulfoselenide or lead selenide. Thephotoconductive material can be vacuum deposited by the thin filmtechniques or electrostatically sprayed by the thick film techniques.The layer of photoconductive material 18 is then sintered'for a periodof time.

A layer of resistive black 16 is depositedover lattice 12 and substrate22 on the front of panel 10. Resistive black 16 could be some materialthat is relatively inexpensive and has a high emissivity, such as carbonslurry type paint.

Refer now to FIG. 3 which illustrates a schematic diagram of theelectrical circuit formed by the inventive panel 10. A voltage source 24is connected across front and back conductive lattices 12 and 20 withthe polarity as shown. Completing the electrical circuit as shown withreference to FIGS. 2 and 3 is the photoconductive material 18, theconductor hole 14, and resistive paint 16. The resistance of material 18varies inversely with the amount of light from the visible imageimpinging on each square of lattice 20. Even though there is only onevoltage source 24 used to apply a potential differences on lattice 12and 20, the schematic as shown in FIG. 3 is an electrical circuitrepresenting only one of the squares included within the lattices. Thereare, in effect, many electrical circuits with each electrical circuitrepresenting one square cell, with the current flow through thatindividual circuit varied in proportion to the resistance of 18.

In the operation of panel 10, a visible light image impinging onphotoconductive material 18 varies the resistance of the photoconductormaterial 18, thus modulating the current flowingthrough the infraredemitting resistive black 16 of the electrical circuit. For example,

sponding juxtaposedsquare on the front of panel 10. A

current increase through this individual cell of resistive black 16causes an increase of infrared energy emitted therefrom. Clearly theincrease in visible light in a specific pattern on the back of panelalso causes increase of infrared radiation from resistive black 16 inthe same specific pattern, thus effecting the technique of transferringand amplifying a direct visible-toinfrared image in life size, or nearlife size.

In one use of such a large panel as that disclosed herein, slides orview graphs of tactical targets, such as the replica of an enemy tank interrain, may be projected on the back of the panel with the resultantthermal or infrared radiation image being emitted from the front. Theemitted infrared radiation may then be observed by infrared imagingsystems. Many slides may be used with a projector for projectingseparate images on the back of the panel. Other uses for panel 10 may bein the medical field where a camera takes thermal graph pictures toestablish cold zones of the body to detect, for example, breast cancer,tumors, varicose veins, etc. The pictures that display lighttransparencies where the cold zones are located may then be projected onthe back of panel 10 to emit thermal or infrared images out the front ofpanel 10. Man other uses of transparent films that record a pattern ofdensity or of temperature conditions, etc., may be used with panel 10for displaying an infrared image therefrom.

I claim:

1. A panel for converting a visible light image to an infrared energyimage, the panel comprising:

a matrix of individual cells mounted on a common substrate;

a front conductive lattice;

a back conductive lattice, said front and back conductive latticesinter-connected on said substrate to form said matrix of individualcells;

a plurality of individual conductors positioned through said substratewherein each of said conductors is associated with an individual cell;

a power supply, said power supply connected between said front said backconductive lattices for applying an electrical charge equally acrosssaid individual cells;

a layer of photoconductive material deposited over said back conductivelattice and the side of said substrate adjacent thereto; and

an infrared emitting substance deposited over said front conductivelattice and the side of said substrate adjacent thereto whereby anincrease in light flux on the photoconductive material at each of saidcells will decrease the resistance between said electrically changedlattices associated with each of said cells thereby increasing currentflow through each of said infrared emitting surfaces associated witheach cell for causing increased infrared radiation from said emittingsurface in a pattern identical to an image effected by modulation ofsaid light flux on the photoconductive material.

2. A panel as set forth in claim 1 wherein said substrate is dielectricmaterial.

3. A panel as set forth in claim 2 wherein said dielectric material isepoxy.

4. A panel as set forth in claim 1 wherein said front and backconductive lattices are square copper grids juxtaposed directly oppositeeach other on said substrate.

5. A panel as set forth in claim 1 wherein said photoconductive materialis cadmium sulphide.

6. A panel as set forth in claim 1 wherein said photoconductive materialis cadmium sulfoselenide.

7. A panel as set forth in claim 1 wherein said photoconductive materialis lead selenide.

8. A panel as set forth in claim 1 wherein said infrared emittingsubstance is resistive black.

9. A panel as set forth in claim 8 wherein said resistive black is acarbon slurry paint.

10. A panel as set forth in claim 1 wherein said plurality of individualconductors positioned through said substrate is a plurality of holeswith an eyelet of liquid aluminum placed therein.

11. A panel as set forth in claim 10 wherein said plurality ofindividual conductors are positioned through said substrate to emergetherefrom in said photoconductive material and said infrared emittingsubstance at an equidistance from said front and back conductivelattices.

12. A technique for transferring and amplifying a visible image to aninfrared image, the technique comprismg:

modulating visible light on a photoconductive material coveredconductive lattice that is mounted on one side of a dielectricsubstrate;

converting said visible light into electrical energy within saidphotoconductive material;

transferring said converted electrical energy through a plurality ofelongated electrical conductors positioned through said dielectricsubstrate to an infrared emitting substance conductive lattice; andconnecting a voltage source across said photoconductive material coveredconductive lattice and said infrared emitting substance coveredconductive lattice whereby said modulating visible light modulates powerfrom said voltage source within said infrared emitting substance foremitting infrared radiation in proportion to the intensity of saidmodulating visible light.

* III Al

2. A panel as set forth in claim 1 wherein said substrate is dielectricmaterial.
 3. A panel as set forth in claim 2 wherein said dielectricmaterial is epoxy.
 4. A panel as set forth in claim 1 wherein said frontand back conductive lattices are square coPper grids juxtaposed directlyopposite each other on said substrate.
 5. A panel as set forth in claim1 wherein said photoconductive material is cadmium sulphide.
 6. A panelas set forth in claim 1 wherein said photoconductive material is cadmiumsulfoselenide.
 7. A panel as set forth in claim 1 wherein saidphotoconductive material is lead selenide.
 8. A panel as set forth inclaim 1 wherein said infrared emitting substance is resistive black. 9.A panel as set forth in claim 8 wherein said resistive black is a carbonslurry paint.
 10. A panel as set forth in claim 1 wherein said pluralityof individual conductors positioned through said substrate is aplurality of holes with an eyelet of liquid aluminum placed therein. 11.A panel as set forth in claim 10 wherein said plurality of individualconductors are positioned through said substrate to emerge therefrom insaid photoconductive material and said infrared emitting substance at anequidistance from said front and back conductive lattices.
 12. Atechnique for transferring and amplifying a visible image to an infraredimage, the technique comprising: modulating visible light on aphotoconductive material covered conductive lattice that is mounted onone side of a dielectric substrate; converting said visible light intoelectrical energy within said photoconductive material; transferringsaid converted electrical energy through a plurality of elongatedelectrical conductors positioned through said dielectric substrate to aninfrared emitting substance conductive lattice; and connecting a voltagesource across said photoconductive material covered conductive latticeand said infrared emitting substance covered conductive lattice wherebysaid modulating visible light modulates power from said voltage sourcewithin said infrared emitting substance for emitting infrared radiationin proportion to the intensity of said modulating visible light.